It’s hard to find a docuseries that’s as infuriatingly twisting as The Staircase. Over the course of 15 years, 13 hours, and three separate parts, director Jean-Xavier de Lestrade has constructed a winding portrait of Michael Peterson, a man who was accused of killing his second wife Kathleen Peterson. The docuseries somewhat exhaustingly shifts between Peterson’s guilt and innocence in a way that brilliantly mirrors Peterson’s trial. However, one of the most shocking elements of this ever surprising docuseries doesn’t happen on camera at all. It was a romance that happened behind the scenes.

In December of 2001, Michael Peterson called the fire department after finding his wife Kathleen Peterson dying at the foot of their staircase. Peterson was accused of murdering his wife, and the case ultimately went to court. That trial is what the first eight episodes of 2004’s The Staircase explore. 2012’s sequel to the original docuseries and Netflix’s recently released three episodes follow Peterson’s life after he was convicted for Kathleen Peterson’s murder. Through a series of events that are as complicated and insane as the original trial, Peterson was eventually released from prison after accepting an Alford plea for the manslaughter of Kathleen Peterson.

But in a recent interview with the French publication L’Express, de Lestrade revealed something even more shocking than his documentary subject’s ultimate fate. Michael Peterson once had a relationship with Sophie Brunet, one of The Staircase‘s editors, while they were working on the series.

“This is one of the incredible things that happened during those 15 years,” the director said. “Life is really full of surprises. They had a real story, which lasted until May 2017. But she never let her own feelings affect the course of editing.”

Brunet has also worked on other big-name projects such as the emotional romantic drama Blue Is the Warmest Color, the French comedy series Call My Agent!, and the French miniseries Jeux d’influence. Brunet’s IMDB page only lists her as working on one episode of The Staircase from the docuseries’ original eight-episode run — 2004’s first episode, “Crime or Accident?”

In the same interview, de Lestrade spoke openly about his relationship with Peterson, clarifying that he doesn’t want to use the word “friendship.”

“I tried to imagine scenarios where he would be guilty. There are many elements that push to imagine. Michael Peterson is himself quite disturbing,” he said. “But after having quietly examined all the elements of the file, having visited the scene, seen the blood on the walls, I have this real impression that it is not a crime.”